In some applications it is desirable to have a video display system which is capable of displaying information received from sources which have both linear and digital signals. One example of such a display system is in the use of forward looking infrared sensors aboard search and rescue helicopters to assist in the detection of lost persons. In such systems the forward looking infrared detectors have typically a single linear monochromatic signal, while the graphics which are displayed on the same display screen, come from a source with three color digital signals.
In the past, there have been both linear video amplifiers for amplifying linear video signals and digital video amplifiers for amplifying digital video signals. Normally, these video amplifiers are not able to perform with input signals that have both linear and digital components. The digital amplifiers are only able to operate at certain preselected discrete output levels and thereby are unable to amplify linear video signals. The linear amplifiers of the past have typically operated at a slow frequency and were unable to handle the very high data rates typically associated with digital video signals. As a result, it has been difficult to use a single video amplifier to amplify both linear signals and high frequency digital signals.
One approach has been used in the past which includes a very high speed linear video amplifier which is able to accommodate the high frequency digital signals as well as the linear signals.
While such a system, or variations of it, have enjoyed some use in the past, it does have several serious drawbacks. First of all, a linear amplifier that operates at a sufficiently high frequency to handle the typical digital video data rates is usually higher in cost than a digital amplifier or a low frequency linear amplifier. Secondly, such high speed linear video amplifiers have an additional cost in that they consume more power than a low frequency linear amplifier.
Consequently, there exists a need for improvement in video amplifiers which are able to amplify a video signal which has both a linear and a high data rate digital video component.